A6 on a Fujitsu means the indoor fan is not turning as the board has asked. The board sends a speed request and expects the motor to confirm it, and when that confirmation stops arriving the unit shuts the indoor section down. You usually notice the room going still before the code appears, because the compressor can keep running while no air moves at all.
The indoor fan is the only part of a split system that runs every hour the unit runs, so its bearing carries more hours than anything else in the machine. Wear shows up first as a faint rumble on start up, then as a motor that takes longer each time to reach speed. By the time A6 appears the bearing is usually gone.
A barrel fan collects dust on the leading edge of every blade, and over a few seasons that build up is thick enough to unbalance it and load the motor. A blade with a leaf or a piece of packaging caught in it does the same in one hit. The motor is asked for a speed it can no longer reach, and A6 is the result.
The fan motor takes its power and its speed signal through one plug on the indoor board. A pin that has backed out of that plug, corrosion from condensate, or a conductor rubbed through where the harness passes the casing will all produce A6 on a motor that is mechanically fine. It is the cheapest of the three to rule out.
Power off, then turn the barrel by hand through a full rotation. It should move smoothly with no tight spot, no rubbing against the housing and no side to side play in the shaft. Dust is cleaned off the blades rather than just the housing. A barrel that rocks on its shaft is a motor or bearing problem, not a cleaning one.
The motor is checked for continuity across its windings and for a bearing that drags when turned. Where the motor spins freely but the board still reports a fault, the speed sensor built into the motor is the likely failure. Confirming that before ordering a part is what stops the same code returning on a new motor.
The plug at the indoor board is released, examined for corrosion and pushed fully home until it clicks. The harness is then followed along its run looking for a pinch, a rub mark or rodent damage. Continuity is checked on each conductor. On an A6 that comes and goes with vibration, this is usually where it is found.
If the blades are clean, the motor turns freely and the wiring is sound, the next step is measuring the board output rather than changing parts. A technician can confirm whether the board is failing to send the signal or the motor is failing to return it. That distinction decides which of the two gets replaced.